The word that describes the process of making an area more densely populated is:
b) populate
The word "populate" refers to the process of making an area more populated. This term can mean to place more people in an area or to have more people move to that area. For example, new housing projects or job opportunities in a city or region can lead to more people settling in that area and an increase in its population. This situation is expressed as the area becoming more crowded or densely populated.
